In current cellular communication systems, a mobile station communicates with a base station. The mobile station must be located within a predetermined distance from the base station. In IS-95 cellular systems, an implementation limitation of 55 kilometers has been set. Consequently, a mobile station must be within 55 kilometers in order to communicate with a base station.
When a mobile station is distant from its serving base station, the propagation delay can become significant. If the power at the mobile station is sufficient to reach the base station, the limitation comes from the ability of the base station to find the signal transmitted by the mobile station from the distant location. In IS-95 systems, a base station typically searches for energy within an interval of +/-226 PN chips, which translates to about 0.184 ms. This corresponds to a distance of about 55.176 km. Beyond this distance, the searcher can not see the mobile station's transmitted signal.
However, when the mobile station has enough power to reach the base station, the inability to communicate is caused by the inability of the base station to find the signal within a predetermined search window. Thus, a need exists for a method for extending the cell radius between a mobile station and a base station.